The assembly of rotor blades on wind turbines and their transport to and fro is a time-consuming, relatively dangerous and also costly task. Prior art gripping devices (also referred to as yoke) often consist of a frame and a number of straps which are wound around at least part of the rotor blade to hold the rotor blade in place. This involves a lot of manual assistance: the frame has to be directed towards the rotor blade very exactly so that the rotor blade fits into the frame. Further, the straps have to be wound around the rotor blade and also unwound manually which involves work at substantial heights. Technicians are typically lifted to the assembly height by a basket from which they operate during the assembly or disassembly of the rotor blade.
For instance, international patent application WO 2011/050999 A1 shows a solution of a dismounting system of a rotor blade of a wind turbine. The system comprises a stable main frame and a strap moving mechanism connected to the main frame. The strap moving mechanism leads the strap around the rotor blade by means of a number of beams that temporarily hold an end portion of the strap to lead it from one side of the rotor blade to the other side along about a half circle. For that purpose, the beams are tilted in several tilting directions in order to eventually encompass the rotor blade partially.
Generally, it is a problem to connect a blade gripping device to a rotor blade because when placing the blade gripping device upon the rotor blade in a correct position in which the blade gripping device fits to the rotor blade and vice versa; a lot of manual adjustment must be done. The blade gripping device can be positioned relative to the rotor blade by maneuvering a crane or other lifting device which holds the gripping device and/or by using and moving taglines attached to the blade gripping device. For instance, such taglines can be pulled manually and/or by winches.
Staff must also be close to the site where the connection of the blade gripping device and the rotor blade takes place, as a visual control is necessary. This requirement is already complicated when the rotor blade is positioned on the ground, but by far more so when it is assembled on a rotor of a wind turbine, i.e. when it is to be disassembled from that rotor in substantial heights which may well exceed 80 meters.
At the same time, it must be guaranteed that the rotor blade is not damaged during the connection process and while it is lifted when using the blade gripping device.